The invention relates generally to power-driven conveyors and more particularly to belt conveyors having retractable flight members.
Many conveying applications require that conveyed articles be spaced apart on a conveyor belt. For example, merging two or more flows of articles into a single file without collisions is a common requirement. One conveyor used to accomplish this without slowing the belt or using complex sensors and external spacing bars is described in U.S. Pat. No. 7,770,718, “Systems and Methods for Providing an Improved Timing Conveyor,” Aug. 10, 2010, by the applicant of this application. The disclosure of that application is incorporated into this application by reference. The conveyor includes a conveyor belt, belt rollers, and flights. Lower surfaces on the rollers engage a roller-engagement surface below the belt. Upper surfaces of the rollers define a plane above the belt. As the belt advances, the rollers roll on the roller-engagement surface and rotate to move an article supported on the rollers forward along the plane. The flights, which are spaced apart along the length of the belt, include cams that engage a cam surface below the belt to impart a moment on the flight and projections that respond to the moment by rotating from a retracted position to an extended position blocking the further advance of an article propelled forward. The cam-actuated flights, in conjunction with the article-accelerating rollers, cause conveyed articles to be staged at known locations on the belt for proper merging. The flights assume a retracted position as they return from the returnway before they encounter the cam surface. A conveyed article resting atop a retracted flight before it is raised to the extended position prevents the flight from popping up by cam action until the article is pushed clear of the flight by the rollers.
Another version of a retractable flight with a clutch mechanism that exerts a low torque on the flight to rotate it up to the extended position is described in U.S. Pat. No. 7,775,345, “Conveyor and Belt with Clutch-Driven Flights,” Aug. 17, 2010, also to the applicant of this application. The disclosure of that application is incorporated into this application by reference. When a conveyed article—even a lightweight envelope—is atop a retracted flight, the low torque provided by the clutch is insufficient to raise the flight from its retracted position. This prevents lightweight articles from leaning from the top of an extended flight without enough frictional contact with the belt rollers to clear the article from the flight, which disrupts the regular positioning of articles on the belt.
In some instances, the bottoms of articles, such as boxes, have loose flaps, flaps glued out of position, or other steps, or discontinuities, which can catch on the edge of the flights in their extracted position. When an article catches on a flight, the conveyor can jam or the article can rotate out of its preferred orientation.